Good questions,
@Twowaxhack.
First the reasoning why we did this ourselves: no electrician would touch this without a full and complete panel replacement. In addition to the panel and the necessary rewiring, it also would require work on the outside of the home. From the meter box, a steel conduit would need to be added with a weather head, and the line from the drops (currently 100A) would need to be changed from the weather head down to the meter box. In addition, the electricians would need to meet current code which would be two ground rods installed, as well as an external outside disconnect (this is local code so the firemen can shut off power.) This is a local thing as the meters are locked to their box; not a simple wire seal, but an integral LOCK. In order to pull the meter, a fireman would have to break the meter. So now local code adds an external disconnect. The drops from the pole were already upgraded to 200A when the transformer blew up a couple of years back. All this work in and outside of the home STARTED at $4k. My dad turned 100 on Tuesday; the house reverts to his wife's grandchildren upon his passing. So NO reason for us to invest much in this. Anyone moving into the house after my dad would perform a gutting of the kitchen and baths, removal of the oil burner, and a LOT of other work. Perhaps a total gut job and renovation. Wouldn't surprise me to see a $200K+ Reno on this.
But speaking of investment, the 10 gauge wire was about $150, the breaker box about $16, the breaker $20, and the disconnect about $10. The water heater was $450. He's filled his oil tank 3x this year, the last fill about $700. So, the cost of one fill pays for all of this. The local electric company is owned by the town; thus is a non profit. They return any surplus to its customers. So, rates are low. The oil burner is the original "tankless"; pretty much any time you use hot water it comes on. The burner isn't modulating; it's on or off. Burns the same rate of oil whether you are taking a shower or heating the home in January when it's 5 degrees outside.
We only needed one 30A circuit for the water heater, so that's why we added the small breaker sub panel with only the one double pole, 240V 30A breaker.
The main panel is a FUSE BOX so I'll call it that to distinguish your thinking from a breaker or service panel. This 100A fuse box, made by Murray, presupposes ONLY two double pole 240V circuits. One for the range, and one for the dryer. These are fed by large cartridge fuses. There are THREE of these cartridge fuse blocks: one 100A for the main that goes direct to the buss bars, one 60A for the range, and one 30A for the dryer. No others are possible at all, even if you don't have the rest of the panel full. The rest of the panel is for single pole, Edison type screw in fuses.
One wiring scheme here would have been change the dryer block from 30A to 60A cartridge fuses, run the appropriate wire (4 or 6 gauge) over to a sub panel, add TWO dual pole breakers, each 30A, one for the dryer and one for the new water heater. This was a bit more work that what we did, and would require another 30A breaker and a larger box with more than two positions. We were kind of relying on what we could locally find. Then we'd have to remove the dryer circuit from the main panel and move it to the new sub panel.
Luckily THIS panel had screw terminals for the buss bars. So I ran the sub panel off these screw terminals on the buss bars. It was the simplest and easiest solution. If the house were my dad's or mine, I'd change the entire electrical system. I'd get rid of the oil burner and put in a heat pump, and add central a/c. Right now people who have these homes in New England built in the 1970s and prior do not have central air, and there is plenty of times in the summer, particularly on a two story home, where it's just too damned hot. Oil is messy. The radiant baseboard heat is great but doesn't allow for a/c. New homes in the area don't use oil burners--all new HVAC designs.
Seriously, we are just three people that seem to eat many small meals around the clock and never reuse anything. If it were up to me, I'd treat everything like I do my coffee cup: It never gets washed and the thicker the coating of brown sludge the better the taste. I learned that from my time in the Navy.
